Note: Descriptions are shown in the official language in which they were submitted.
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Rl~SISTOI~ INS~:R'rION 1'USE
BACKGROUNI) OY THE INVE~TION
Field of the Invention
The present invention pertains to a fuse for insertion in the
primary circuit of a high voltage transformer or other device and
having a rupturable element wire which melts at a predetermined
current level. The fuse includes an arc intercepting element and a
resistor in circuit with the intercepting element to reduce fault currents
momentarily to an arc extinguishing level to clear the circuit.
Background Art
In the art of protective fuses ~or electrical circuits and the
like, and in particular for high voltage transforrner circuits, it is
known to provide so-called protective links to remove an internally
faulted transformer from the primary line thereby preventing outages to
other circuits on the line no-t served by the fa-ulted transformer. The
conventional approach to providing circuit clearing fuses for faulted
transformers and other high voltage circuits has included the provision
of a fuse having a component wllich melts or decomposes to produce an
arc exting~ishing gas to eliminate continue(t arcing. l-lowever, the
conventional silver/ sand current limitillg fuses are experlsive and it has
been impractical to equip distribution transformers with this type of
use. At the same time, there has been an incrensillg number of
systems wherein potential fault curren-ts ale much higller than previous
fuse designs are capable of interruptirlg wit1lout some dallger to
equipment and to the en~rironment surro~ di11g the h~ans~ormer itse1t`.
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IL has been determirIed th.lt convelltional wcak link type
current limitingr fuses which, for example, ope-rate by utilizing gclS
pressure to propt?I one end of the fuse structure ~way from the other
end in an oil filled transf`ormer to provide c;rcuit interruption, ha~e
been foun~ to be suitable for fault currents in the range of 150û amps
or less. For higher fault currents it has become necessary to
strengthen the mechanical structure of the fuse, as well as the support
bushing for the fuse. This has become increasingly expensive and a
not entirely satisfactory solution to failures wherein fault current3 in
the range of 3,000 to 35,000 amps may occur.
Accordingly, since the conventional rupturable element type
f'use, provicled with a material such as a vulcanized fiber tube
surrounding the fuse element to provide the arc extinguishing gas, has
been relatively successful for current levels in the range of 100 to 1500
amps, it has been determined tha-t it is desirable to provide for a fuse
structure which will insert a resistor in the circuit on failure o~ either
the transforrner or any other short circuit which rnight occur wi-thin the
transformer enclosure~ The object of the present invention is -to
provide ~or directing the arc established upon melting of the fuse
element in such a way tha-t it passes -through a resis tor to at least
momentarily reduce the current level to a value which will result i
extinguishment of the arc in the presence of a deionizing gas. This
functional advan-tage is provided by structure w]-lich has heretofore not
been provided in the art of protec-tive link fllses i`or trnnsforlIlers ancl
the like. Moreover, -the particular arrangement vf n protective fuse in
accordance with the present invention also provicles, ill one compact
structural unit, the capability of protecting the circuit ngailIst sllort
circuit condiiions when the current is nt a ~elnti~rely k~w le~cl nlI~l upon
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heating of -the resistor whereby sufficierlt mcchani( nl separatioll of the
fuse conductor elements may be obtained to preverlt arc establishmellt
or restrike.
SU~IMARY GF THE INVE~TION
The present invention provides an improved protective linik or
circuit interrupting fuse for relatively high voltage applications,
particularly in the env-ironment of protecting the primary circuit of a
distributicn transformer or the like, wherein an improved arrangement
of a resis-tor element is provided to momentarily reduce the fault
current to a level which will provide arc extinguishment by deionizing
~ases generated by failure of the fuse.
In accordance with one aspect of the present invention, there
is provided a fuse element for a transformer or the like which includes
a fusible link, which upon melting as a result of an overload current,
establishes an arc or sufficien-t energy -to decompose a gas generating
substance. The fuse is also provided with an arc intercepting element
which is in circui-t with a resistor which momentarily reduces the fault
current to a level w}lich will enable the cleionizing gas to ex-tinguish the
arc and to preveIlt restrike.
In accordance with another aspect of the ~reserlt invention,
there is provided ail improved :fuse structure includillg a fusible
element, an arc intercepting element, and a resistor nrrallged in such a
manner that heating of the resistor will cause mechclllical separatioll of
one terminal of the fuse with suf.~icie-rlt .torce to separate the fuse
conductor elements to interrupt or e~-ting-lish aII arc. The fuse is
preferably clisposed in nn arc suppressing~ env;ro.~lmel-lt SUC~I as by
being at least partially immersed in transformer insula-tinog fluid.
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In accordarlce with yet nnother im~)ortarlt aspect o~` the
present invention, there is provided a fuse of a type whicll is adapted
-to be inserted in an insulating bushing which inclulles a main current
carrying member made of a suitable magnetic material which produces a
magnetic field of sufficient strength to control the location of an
electrical arc. The magnetic field produced by -the current carrying
member forces the arc into the vicinity of a gas generating fiber tube
to produce a greater amount of arc extinguishing gas more rapidly than
with prior art protective link type fuses.
The present invention still further provides an improved fuse
construction for use in connection with transformers and other high
voltage devices wherein the fuse is adapted to be immersed in oil and
includes an orifice which allows the interior of the fuse structure to fill
with oil when immersed but is also sized to control the generation of
gas pressure upon failure of the fuse so that a pressure force will
cause certain elements of the fuse to forcibly separate from the
remainder of the fuse structure for greater separation of the conductor
elements to provide arc extinguishmen$.
The overall cons~ruction of the protective linli type use of
the present invention is compact, economical to manufacture and
superior to fuses heretofore known in the art. Those skilled in the art
will appreciate the advantag es discussed herein, as well as other
superior features of the present inventio~l which will become apparent
upon reading the detailed descrip-tion whicll i~ollows in conjunc-tion with
the drawing.
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Blt~IE~` DE~Cl~lYTION Ol~' 'r[ll: Dl~ NC
Figure 1 is a partial e1e~vatioll in sectiorl Or a typical electrical
distribution transformer showing the fuse of tlle prescl-1t invention
mounted in an insulating bushin~,r; and
Figure 2 is a 1Ongitu~ al ceIltral sectiorl view of the fuse of
the present invention.
DESCRIPTIOM OF THE PREFERE~ED !EM~ IMENT
The present invention comprises an expulsion type fuse of the
type to be used in electrical distribution transformers and the like and
which is adaptecl to be placed in series with the high voltage winding of
the transformer to clear the circui-t by generating an arc extinguishing
g^as to interrupt the fault current as the current approaches a zero
point on its wave form. In particular, the -t'use of the present
invention is adapted to provide arc interruption and circuit clearing
without the necessity of increasing the mechanical strength of associated
structure such as, for example, the t ransformer bushing and tank .
Ref'erring lo Figure 1 of the clrawings, there is shown a
portion of a typical electric utility distribution transformer generally
designated by the numeral 10. The transformer 10 includes a tank 12
in which -the transformer windings are disposed ancl covered witll an
insulating and cooling oil 13 svith WhiC}l the tank interiol is t'illed. A
high voltage conductor 15 is connected to tlle -transormer at n porcelain
bushing of a conventional type, designnted by tl1e ~lumel al 1~1, which is
mounted on a top wall or cover portion 17 of the tank a1~d e~tends into
the interior of the tank, as illustrated. The bushing l~1 is provided
with an internal bore 19 in which is rnclllnted n hls~ or protective linl~
in accordance with the present inventio1l ansl gel1ernlly designated by
the numeral 16. A lower portion ot t1le tuse l6 e~tt~nds tr(~ t'le
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bottom end of the bushing and the fuse is su~stantially immersed in the
transformer oil contained within the tank. ~lthough the fuse 16 is
illustrated as being mounted within the high voltage bushing 14, it will
be understood that the fuse may be mounted on a terminal block -,vithin
the transformer tank or on other suitable structure ~.vithin or even
outside the tank. Moreover, the fuse 16 will also operate satisfactorily
in the presence of air or other gaseous insula-ting fluids as well as
liquid insulating fluids including the oil 13.
Referring further to Figure l, the fuse 16 includes an
elongated conductor element or rod 20 wh;ch extends through the top of
the bushing 14 ancl is suitably corlnected to a connector element 22
which in turn is connected to -the high voltage conductor 15.
Referring now to Fig~re 2, in particular, the fuse 16,
inclucling the conductor rod 20, is shown in longitudinal elevation with
a major portion of the fuse shown in longitudinal central section. The
lower end of the conductor rod 20 is -fastened to an elongated tubular
element 24 comprising a vulcani~ed fiber tube of a type which is
adapted to generate a deionizing gas when exposed to a high voltage
electrical arc or other heat generating pherlornena which woulcd tend to
decompose the tube. The tube 24 is of a type cornmercially available
for use in transformer fuses and the like. Tlle tube 24 is snuggly
fitted over -the end of the rod 20 and is securetl -to the rod by a
transverse pin 26 which extends through the rod and through a
suitable diametral hole drilled through opposed portions of the side~,vall
of the tube 24. Directly below the rod 20 is a vent hole ~ whicll is
drilled through the sidewall of the tube 2~ to provicle for controlled
venting of gases from the interior of the tnl e alld to pe~ it the interior
Or the fuse to Mll with insulcltirlg~ tl~lid ~IICI~ a~i t~aln;forme~ oil.
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The~ lower elld of the tuhe 2~1 is provi(le(l with a
circumferential groove 25 which is engaged by a copper or steel tubular
sleeve 30 suitably crimped into the groove as illustrated. Alternatively,
the tube 24 coulcl be pr ovi<led Wit}l tapere~l threads engageable with
cooperating threads formed on the sleeve member 3û. The sleeve 30 is
disposed around and contiguous with an arc intercep-ting member
characterized by a cylinclrical plate 33 having a cylindrical opening
formed in the center -thereof and which is delimitecl by a convex curved
wall portion 35. The r ounde~ surface or wall portion 35 is provided lo
reduce the effects of dielectric stress exerted on the member 33 when
the member acts to intercept an electrical arc, as will be discussed in
further detail hereinbelow. The member 33 may be formed of a suitable
metal conductor material such as brass. Alternatively, the members 30
and 33 could be fabricated as a single piece.
The fuse 16 is still fur-ther characterized by a cylindrical
tubular resistor elemen-t generally designated by the numeral 'lO which
i s fitted within the interior of a depending portivn 32 of the sleeve
member 30 and is connected at its opposite end to a cap 42. The
resistor element qO may be of varied construction sucll as, t'o17 e~amp1e,
a resistive material with wourld wire or, pre terably, a high te~mpernture
material such as silicon carbide . In a preferred embodimerl t of the
present invention, the resistor eleMent 40 is ot` a type commercially
a-vailable from the Carborundum Compally, Niagclra Fnlls, New Yorli as
-their type SP high power non-inductive resistors. Tlle resistor elemen-t
40, for a particular fuse element having the capability nf interrllptillg
fault currents in the range ot` lO0 amps to 3500 amps o~ more, has a
nominal resistance of '1.5 ohms all~l is a type ~Y5 SP 71~5~ the
desig~nati(lrl be;llg tl~.lt of thc al)o~rclllelltio~le~l so~ cc o t` thîs e1t~metlt.
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The r esistor element 40 is secur e(l to tlle mcrrlber 30 at arl ir/terface 37
withiIl the portion 32 by a relatively high temperature sol(ler such as a
cvnventional lead-tin solder having a 40/60 or 50/50 composition of lead
with respect to -tin of which the eutectic point is in the range of
456 F. The element 40 arld member 30 coulcl be provided with other
means such as cooperating threads for securing ti~ese parts to each
other. Tile fuse 16 is also preferably provided with a sleeve member
41 comprising a heat shIinkable fluorocarbon plastic tube disposed over
the sleeve member 30 and extendin~ long~tudinally beyond each end of
the sleeve member 30. The sleeve 41 forms a substantially gas tight
seal and supports the assembled componellts of the fuse 160
The lower end of the resistor eIement 40 is soldered to the
cap 42 which also may ~e made of brass, for example. The resistor
element 40 is secur ed to the cap ~12 by a solder layer 45 having a lower
melting point than the solder used to secure the upper end of the
resistor element to the member 30. For example, a solder comprising
43% -tin, 14% bismuth and 43~ lead with a mel-ting point in the range of
289 to 325 F. is preferably usecl. Tlle use of the lower melting point
solder layer 45 to form the connection between the cap 4~ an(l the
resis-tor element 40 provides for forcible separation of the cap from the
r emainder of the tuse due to mel-ting of the solder upon heating of the
resistor and genera-tion of gas pressure within the interior of the fuse
upon failure of the fuse element itself. In this way, a conclucior ~i
conrlected to the cap 4~ and leadiIlg to the primary windings of tile
transformer, not shown, may be blowrl cleal of the fuse into the
interior of the tank to reduce the possibility of al'C strike or restr;ke in
the event of relatively slow failure of the fuse.
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'rlle fuse 1~ is yet further char.lcteri~e(l by arl elongatcd fuse
element 46 comprised of fuse elemellt wire commorlly used in distribution
transformer fuses and properly sized to provicle for rupt~re such as b~
melting of the wire on e~periencing a fault current greater than a
nominal 5 to 10 times the normal full load current in orcler to remove
the transformer from the systel~ circuit. The fuse element wire itself
lorms no part of the present invention and may be made of conventional
fusible element materials used in distribution transformer fuses. The
element 46 raay be formed of silicon bronze and bc a no. 25 to a no. 12
round AWG siæe wire, for example. The fuse element ~6 is inserted in
a hole formed in the lower end of the conductor rod 20 and is fixed
thereto by brazing, for example. The opposite end of the fuse element
46 is secured to the stranded conductor 44 within the central bore 49
formed in the cap 42 by crimping tlhe sleeve portion 43 of -the cap to
retain the conductor and fuse element 46 in assembly with the cap.
The fuse 16 can also be provided wi-th an elongated thin walled plastic
tube or sheath ! not shown, disposed around the fuse element 46 and
spaced somewhat therefrom but within the bore formed by the tube 24
and the resistor element 4~). Such a tube is adap-ted to surround the
fuse element to confine low Gurrent arcing wi-thin the tube UpOII rupture
of the fuse element 46 but which would burst on relatively high i~lult
currents.
By providing the arc intercepting member 33 nnd also the
resistor element 40 as part of the fuse structure, the improved fuse l(i
of the present invention is operable to direct the electrical nrc
generated upon mel-ting of the I use element 46 in such n way th.lt the
fault current passes through the resistor element 4n alld is momentn~ y
reduced suffic;ently to nllo~Y tlle gnses .~;ellel~nte(l ~tithill a cllam~ er ~7
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Lormed by the bores o~ -the resistor 40 and the tube 24 to e~tinguish
the arc and prevellt arc restrike after the current passes throu~h the
zero point on its wave form. The combination ot the system groundin~
impedance and the resistive irnpedance of the resistor element 40 is
sufficient to reduce fault currents in tile 3,ûO0 to 35,000 arnp range and
higher to values which have been successfully interrup ted using the
technique of arc extinguishment by the generation of a deionizing gas
in the vicinity of the arc. The resistor elemen-t 40 is not a primary
conductor element of the circuit except on separation of the fuse
element 46 ancl establishment of an arc which is intercepted by the
member 33. However, the resistor element 40 is inserted in the circuit
as rapidly as the creation of the arc.
In accordance with another important aspect of the present
invention, by providing the elongated conductor rod 20 of a soft
annealed s-teel such as, for example, SA~ 1019 low carbon steei, the rod
is capable of generating a magnetic field 56 having a flu~ sufficient to
direct an arc generated upon rupture or melting of the fuse element 46
in such a way that the arc remains in pro~imity to the interior of the
fïber tube 24. By forcing the arc against the interior ot` the f`iber
tube, greater amounts of ~leiorlizing gas are quickly generated than
would occur if the arc location were not controlled. At the same time,
the arc is also, of course, directed ;nto con-tact with the intercepting~
member 33 whereby the fault current passes thloug~n the resistor
element 40 to momentarily reduce the curren-t valut? as described nbove.
Another important aspec-t of the structure nnd fllnctioll of the
presen-t invention pertains to the arrangenlent ~vhcrebv tlle intt?rior
chamber ~l7 formed by the boI~es of tll~? tub~? ?,~ t~ ?SiStOl' ~I~?lllt?llL
40 iS SUbStarltiillly sealed (?~ct`l)t t`OI' tll(` Vt`llt h~-le '~8. ~ lC ~it bt'tWeCll
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the concluctor rod 20 an(l the f`iber tube 24 i.s substarltially fluid tight
as is the fit between the tube 41 and the members 24 and 40. 'rhe
conductor 44, which Is preferably of stranded wire, presents
substantial resistance to rapid fluid flow through the bore 49 but has
sufl`icient porosity to allow oil to enter the interior of the fuse.
Accordin~ly, gas generated within the charnber 47 upon failure of the
fuse element 46, is substantially confined to the interior of the fuse
with some controlled venting through the vent hole 28. The vent hole
28 also allows the interior of the fuse to fill with oil or other fluid from
the transformer tank when immersed therein, as illustrated.
Under certain operating conditions, upon failure of tlle fuse
element 46 and shunting of the fault current through the resistor
element 40, the resistor element will be heated sufficiently to melt the
solder 45 joining -the cap 42 to the resistor element. Accordingly, the
pressure generated by the formation of the deioni~ing gas within the
interior of the resistor would forcibly eject the cap 42 from the end of
the resistor element into the transformer tank a suffïcient distance to
prevent sustainment of an arc.
Accordingly, the fuse 16 provides mul-tiple arc extinguishment
features comprising the shunt resistor 40 and -the provision of a
expulsion cap 42 which operates to physically separate the conductor ~ ~
from proximity to -the conductor rod 20 a sufficit-~nt distnllce to ~re-vent
sustainment of the fault current arc. Moreover, the fuse 16 is
arrangecl within the support bushing 14 SUC}I thnt the resistor element
40 extends from the lower end of the busllillg. ~ccordingly, iIl
situations where a fault current arc may bt-~ OCCUl'ritl` Withill the
interior of the transformer tmlk enclosure as causeci ~- eitller over
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move into eontact ~vith the resistor c~(?meilt wheIeby the cireuit is
established through the resistor element ~10 to reduee the arc current
sufficiently to effect extinguishment of the arc.
As indicated hereinabove, tile materials of eonstruetion of the
fuse 16 are of some importanee, including the material used for the
eonductor rod 20. The rod 20 is preferably formed of cold rolled soft
steel whieh has been annealed and plated with a suitable corrosion
resistant plating or eoating. The tube 24 is of a type whieh is known
for use in eonnection witlh fuses for distribution transformers and the
like and is formed of an organie fiber whieh generates a substantial
amount of deionizing gas to counteraet the generation of ionized gas
produced by the arc in the presence of the transformer oil or other
insulating fluid. The provision of the are intercep-ting member 33 of
soft steel or eopper alloy with the eurved surfaee 35 reduces the
dieleetrie stress eoneentration in this element. The resis-tor element 4()
may take variows forms although the type of element described herein is
preferable in that it provides a eompaet and suitable struetural
arrangement for the fuse itself. The partieular eommereial element
deseribed herein is provided with metallized ends to faeilitate l`ixing~ the
resistor element to the sleeve member 30 and to the cap 4'~ by
soldering, as deseribed.
Those skilled in the art of high voltage proteetive dev;ces ~vill
appreeiate from the foregoing that a superior proteetive link has been
provided by the present invelltion ~vhieh is economieal to maIlufcleture,
and is reliable in operation. The fuse 16 inclllcles a numbc?r ot` superior
features which tunctioll in combination to prov;cle t'OI~ c~;rcuit clear;llg in
high voltage and high amperage short cire~lit co~lcl;tions sucll as are
experieneed in a llumbel~ of eleet~ielll dev;ees a~ pa~tieulal~, in
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elcctrical distribution system trarlsformers. Those skilled in the ar-t will
also appreciate that ~arious substitutions and modi~ications may be made
to the present invention without depar-ting from the scope of the
appendeci claims.
What I claim is:
